This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
3GPP third generation partnership project
CA carrier aggregation
CC component carrier
CIF carrier indicator field
CQI channel quality indication
DCI downlink control indication
DL downlink (eNB to UE)
eNB EUTRAN Node B (evolved Node B/base station)
E-UTRAN evolved UTRAN (LTE)
IMT international mobile telecommunications
ITU-R international telecommunication union - radio
LTE long term evolution
LTE-A long term evolution-advanced
MME mobility management entity
MIMO multiple input multiple output
MU multi-user
PCC primary CC (also termed PCell)
PDCCH physical downlink control channel
PDSCH physical downlink shared channel
PUSCH physical uplink shared channel
RLF radio link failure
RRC radio resource control
SCC secondary CC (also termed SCell)
UE user equipment
UL uplink (UE to eNB)
UTRAN universal terrestrial radio access network
FIG. 1 shows the overall architecture of the E-UTRAN system, in which eNBs are interconnected with each other by means of an X2 interface and which provide the EUTRA user plane and control plane (RRC) protocol terminations towards the UE. The eNBs are also connected by means of an S1 interface to a MME and to a Serving Gateway.
Future releases of 3GPP LTE are targeted towards future IMT-Advanced systems, referred to herein for convenience simply as LTE-Advanced (LTE-A) which is expected to be part of LTE Release 10. LTE-A is expected to use a mix of local area and wide area optimization techniques to fulfill the ITU-R requirements for IMT-Advanced while keeping the backward compatibility with LTE Release 8. Topics that are included within the ongoing study item includes bandwidth extensions beyond 20 MHz, relays, cooperative MIMO and multi-user MIMO, and single user MIMO on the uplink.
The bandwidth extension beyond 20 MHz in LTE-Advanced is to be done via carrier aggregation CA, in which multiple component carriers CCs are aggregated together to form a larger bandwidth. This is shown by example at FIG. 1B in which there are 5 Release 8 compatible CCs aggregated to form one larger LTE-Advanced bandwidth. The purpose for aggregating individual 20 MHz Release 8 compatible component carriers (CCs) is that each existing Release 8 terminal can receive and/or transmit on one of the CCs, whereas future LTE-Advanced terminals could potentially receive/transmit on multiple CCs at the same time. FIG. 1B is exemplary; in practice there may be more or less than five CCs, they may not have equal bandwidths, and/or they may be frequency non-adjacent. The CCs could be aggregated in both TDD and FDD systems.
In LTE Release 8, the PDCCH could only be used to indicate a PDSCH/PUSCH sent on its own DL CC or its paired UL CC. In LTE-Advanced, “cross-scheduling” can be available, which means the PDCCH could be used to indicate PDSCH/PUSCH resources sent on other CCs other than its own DL CC and/or its paired UL CC. From the perspective of the transmitted PDCCH this cross-scheduling is useful for distributing traffic loads among the multiple carriers.
One problem in cross carrier scheduling arises in that there are different formats for the PDCCH. Note that 3GPP TS 36.331 v9.3.0 (2010-06) uses the term cell (e.g., PCell or SCell) rather than component carrier. By convention the PCell is the serving cell on the primary component carrier and the SCell is the serving cell on any secondary component carrier. In the case of cross carrier scheduling, a CIF should be included in the PDCCH to indicate which cell (or which CC) is scheduled. Thus depending on whether cross carrier scheduling is used or not the PDCCH format can be different meaning the UE should interpret the PDCCH differently. In case CA is not used, the PDCCH format used will be the same as in LTE Releases 8/9 and it is expected there will be no CIF signaled. The eNB can add a SCell for a UE which has only a PCell configured, and similarly withdraw a SCell from a UE leaving it with only a PCell. In both cases the eNB and the UE each need to have a clear understanding of what PDCCH format is in use at any given time on any given cell.